Intensifier radiographic imaging system

ABSTRACT

An intensified radiographic imaging system comprised of an image intensifier tube including an input screen assembly having means for converting an incident X-ray image into an electron image, an output screen having means for converting the electron image into a visible light image, and an adjacent output faceplate transparent to visible light; a photographic film; means for pressing a portion of the film against the exterior surface of the output faceplate when desired; and means for focusing the entire electron image onto a minified area of the imaging screen and alternatively onto an area of the imaging screen proportionate in size to said portion of the film.

Grossel et al.

[ INTENSIFIER RADIOGRAPHIC IMAGING SYSTEM Inventors: Stanley S. Grossel, New York, N.Y.;

Andrew L. Cunningham, Springfield; H. Sherwood Cooke, Stamford, both of Conn.

The Machlett Laboratories, Incorporated, Springdale, Conn.

Filed: Mar. 5, 1973 Appl. No.: 337,817

Assignee:

250/320, 321, 275; 313/65 R; 95/l R, 12

References Cited UNITED STATES PATENTS [11] 3,835,314 [451 Sept. 10,1974

3,303,345 2/ 1967 Wolms 250/213 VT 3,356,851 12/1967 Carlson 250/213 VT 3,675,027 7/1972 Tsuda et a1. 313/65 X Primary Examiner-Walter Stolwein Attorney, Agent, or Firm-John T. Meaney; Harold A. Murphy; Joseph D. Pannone [57] ABSTRACT An intensified radiographic imaging system comprised of an image intensifier tube including an input screen assembly having means for converting an incident X-ray image into an electron image, an output screen having means for converting the electron image into a visible light image, and an adjacent output faceplate transparent to visible light; a photographic film; means for pressing a portion of the film against the exterior surface of the output faceplate when desired; and means for focusing the entire electron image onto a minified area of the imaging screen and alternatively onto an area of the imaging screen proportionate in size to said portion of the film.

15 Claims, 7 Drawing Figures INTENSIFIER RADIOGRAPHIC IMAGING SYSTEM BACKGROUND OF THE INVENTION This invention relates generally to image intensifier systems and is concerned more particularly with an imaging system having an image intensifier tube in combination with recording media. I

It is well-known that an X-ray beam passing through a portion of a patients body is modified in accordance with a density pattern formed by the internal organs, bone structure and tissues. Consequently, the emerging beam conveys an X-ray image which can be revealed by having the modified X-ray beam impinge on suitable recording media, such as X-ray film, for example. The resulting visible image is of prime importance in locating any abnormalities and in forming an accurate diagnosis of the patients condition. Therefore, efforts have been made to increase the information available in the image by increasing brightness, contrast and resolution, without significantly increasing the intensity of the irradiating X-ray beam.

One prior art type of X-ray imagining device comprises an image intensifier tube having an input screen assembly disposed to receive an X-ray image of an irradiated subject. The input screen assembly generally includes a photocathode which emits electrons in a spatial distribution pattern corresponding to the X-ray image. Consequently, there is produced an equivalent electron image which is accelerated and focused onto an imaging screen much smaller in size than the photocathode. The imaging screen usually comprises alayer of phosphor material which fluoresces locally in direct porportion to the intensity of impinging electrons whereby producing a bright visual image. The brightness of this minified image is due partly to the reduction in size of the emitted electron image and partly to the kinetic energy imparted to the electrons in the image when they are accelerated from the photocathode to the imaging screen. Thus, the described image intensifier tube provides a visual image which is smaller but many times brighter than a visual image produced by conventional fluoroscopic techniques.

The bright minified image, thus produced, generally is viewable directly through an adjacent outputfaceplate of the tube with the aid of suitable magnifying optical devices or a TV camera tube, for example. The output image also may be photographed with a conventional camera having a suitable magnifying lens system.

. In many instances, it is desirable to have means for viewing the output image directly and for recording the output image on film. Consequently, prior art'radiographic systems of the described type generally provide a beam splitter, such as a semi-transparent mirror, for

example, which delivers a portion of the light in the' output image to a direct viewing device, such as a TV camera, for example, and the remainder of the light to a photographic camera. However, the necessary optical devices for splitting the beam and magnifying the output image to film-size generally degrade image resolution and result in a significant'loss of image intensity.

Therefore, it would be advantageous and desirable to have an intensified radiographic imaging system which permits direct viewing of th output image and permits recording of the image on film without requiring intermediate optical devices.

A SUMMARY OF THE INVENTION Accordingly, this invention provides an intensified radiographic imaging system comprising an image intensifier tube which produces a bright minified image fordirect viewing and alternatively a film-size imagefor recording on photographic film.

The image intensifier tube of this invention includes an elongated envelope having at one end a radiation photocathode emits electrons from incremental areas thereof in direct proportion to the intensity of incident light photons thereby producing an equivalent electron image.

Disposed within the tube envelope and adjacent the output faceplate is an output fluorescent'screen and an axially aligned, anode electrode. The anode electrode is maintained at a high positive potential with respect to the photocathode for the purpose of establishing a strong electrostatic field which accelerates the emitted electrons towards the output fluorescent screen. Consequently, the accelerated electron image passes through the anode electrode and impinges on theoutput screen with sufficient energy to cause it to fluoresce locally in accordance with the intensity of the incident electrons. As a result, the output screen produces a bright visible image which is viewable directly through the output faceplate of the tube.

Disposed between the photocathode and the anode is a coaxially aligned series of spaced grid electrodes having appropriate respective configurations for focussing the electron as desired. With suitable potentials applied to the grid electrodes, the emitted electron image may be focused onto a minified area, such as one inch in diameter, for example, of the output screen to produce a corresponding size visible image having optimum brightness for direct viewing. By applying other suitable potentials to the grid electrodes the electron image may be focused onto a larger effective area such as 4 inches in diameter, for example, of the output screen thereby improving image resolution but decreasing image intensity.

External means are provided adjacent the output face-plate for aligning a photographic film of suitable size, such as four inches by four inches, for example, with the output faceplate when desired and for urging the film flat against the exterior surface of the output faceplate while the film is being exposed to the output image. Thus, when it is desirable to record the output image on a photographic film, theminified output ,output image reaches the photographic film thereby producing a bright clear picture of the image. In this manner, optimum resolution of fine structural detail is achieved for the size of the film being used without re- 3 I quiring intermediate magnifying optical devices which degrade image resolution, contrast and intensity.

BRIEF DESCRIPTION OF THE DRAWINGS For a-better understanding of this invention, the following more detailed-description makes reference to the accompanying drawing wherein:

FIG. 1 is an axial view, partly in section, of an intensifier radiographic imaging system embodying this invention;

FIG. 2 is a schematic view of the image intensifier tube shown in FIG. 1 producing aminified visisble image;

FIG. 3 is a schematic view of the imageintensifier tube shown in FIG. 1 producing a film-size visible image;

FIG. 4 is an end view of the imaging system shown in FIG. 1 in the direct viewing mode of operation;

FIG. 5 is an end view of the imaging system shown in FIG. 1 in the film recording mode of operation;

FIG. 6 is an enlarged fragmentary cross-sectional view taken along the line 66' in FIG. 4 and looking in the direction of the arrows; and

FIG. 7 is an enlarged fragmentary cross-sectional view taken along the line 77 in FIG. 5 and looking in the direction of the arrows.

' DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing wherein like characters of reference designate like parts throughout the several views, there is shown in FIG. 1 an intensified radiographic imaging system'comprising a radiation generator. 10, such asa conventional X-ray tube, for example, which is disposed to beam radiation through a preselected .portion of a subject 12. The beam emerging from the opposing side of the subject 12 conveys a radiational image of the preselected portionto the input end of an image intensifier tube 14.

The image intensifier tube 14 comprises an elongated envelope 16 having at one end a cathode sleeve 18 made of conductive material, such as Kovar, for example. The sleeve 18 terminates at one end in an outwardly extending annular flange 19 which constitutes the cathode terminal of the tube 14. The opposing end of sleeve 18 is peripherally sealed to one end of a hollow cylinder 20 made of dielectric material, such as glass, for example, which is provided with a reentrant tubular extension 21. The extension 21 comprises an exhaust tubulation whereby the tube 14 is evacuated during fabrication and which is sealed off, in a wellknown manner, after processing of the tube is completed. The other end of dielectric cylinder 20 is peripherally sealed to one end of an anode sleeve 22 made of conductive material, such as Kovar, for example. Anode sleeve 22 terminates at its other end in an outwardly extending annular flange 23 which constitutes the anode terminal of tube 14.

Cathode terminal 19 is hermetically attached, as by welding, for example, to an outwardly extending flanged end portion of a metal sleeve 24 which is coaxially disposed within the cathode sleeve 18. The sleeve 24 is circumferentially sealed to the periphery of a faceplate 26 which closes the output end of the envelope 16 and may comprise a thin membrane of radiation transparent material, such as glass, for example. The faceplate 26 may be provided with a substantially spherical contour and may have a diametric dimension in the range of 6 to 14 inches, for example.

Supported adjacent the inner surface of faceplate 26 is an input screen 28 comprising a radiation sensitive layer of fluorescent material, such as silveractiv'ated zinc cadmium sulfide, for example. The fluorescent material of input screen 28 may be deposited'directly on the inner surface of input faceplate 26, for example, thereby providing the input screen with a conformingly shaped contour. Thus, the incoming radiational image, after passing through the faceplate 26, impinges on the input screen 28 causing it to fluoresce locally in accordance with the intensity of incident radiation. As a result, the input screen 28 produces a corresponding visible light image which impinges on an axially aligned photocathode 30.

The photocathode 30 comprises a layer of photoemissive material, such as cesium antimonide, for example, which may be deposited on the inner surface of the input screen 28 whereby "the photocathode is provided with a conformingly shaped contour. In instances where the fluorescent material of input screen 28 is found to be incompatible with the photoemissive material of photocathode 30, a thin transparent film 32 of mutually compatible material such as aluminum oxide, for example, may be disposed therebetween. Consequently, the light'photons emanating from the input screen 28 pass through the film 32 and impinge on aligned incremental areas of the photocathode 30. As a result, the photocathode 30 emits electrons from discrete areas of its inner surface in direct proportion to the intensity of impinging light photons, thereby producing an equivalent electron image.

Thus, the input screen 28 and the photocathode 30 comprise an input screen assembly 34 which converts an incoming radiational image into a corresponding electron image. The input screen assembly extends radially over the inner surface of faceplate 26 and, electrically contacts an inwardly extending flanged end portion of metal sleeve 24. Depending from the opposing surface of said flanged end portion is a metal skirt 36 which aids in shaping electrostatic field surfaces adjacent the photocathode and also shields the sealed joint between the cathode sleeve 18 and the dielectric cylinder 20. The skirt 36 extends longitudinally of the tube and terminates adjacent one end of a spaced grid electrode 40 comprising a tapering metallizedinner surface portion of envelope 16. The grid electrode 40 is electrically connected to a first grid terminal member 42 which extends hermetically through the wall of dielectric cylinder 20 in a well-known manner. Thus, the

first grid electrode 40 comprises a hollow conductive cylinder extending longitudinally of the tube and tapering radially inward to a smaller diameter end portion.

Coaxially disposed within the smaller diameter por- I 49 is curved back on itself, in the well-known manner,

fining opening 60 and a smaller diameter end to provide a smooth rim defining a central opening 50 of predetermined diametric size, which is axially aligned with the photocathode 30.

Flange 49 is attached to one end of a dielectric support ring 52 which is attached at the other end to an annular flange 57 of a third annular grid electrode 54. Flange 57 extends inwardly fromone end of a longitudinally extending, hollow cylinder 58 and terminates in a smooth circular rim which defines a central opening 60 axially aligned with opening 50 and having a diametric size approximately equal thereto. The other end of cylinder 58 is provided with an inwardly extending, annular flange 59 which terminates in a smooth rim defining a central opening 62. The opening 62 is axially aligned with opening 60 but is of relatively smaller diametric size. The grid electrode 54 is electrically connected to a third grid terminal 56 'of the tube, whereby the respective flanges 57 and 59 are maintained at the same electrical potential. Thus, the described grid electrode 54 may be replaced by a hollow, frustoconical electrode, for example, having large diameter end de- I defining opening 60. I I

An inner, longitudinally extending portion of dielectric cylinder is attached, by conventional means, to flange 59 thereby supporting third grid electrode 54, dielectric ring 52 and second grid electrode 40. The flange'59, in turn, supports a dielectric ring 64 which is attached to a first decelerator electrode 66. Decelerator electrode 66 is electrically connected to a first deceleration terminal 68 of I the tube, and comprises a conductive ring defining a central opening 70 which is axially aligned with the opening 62 and relatively larger in diameter. The decelerator electrode 66 is longitudinally spaced from one end of a coaxially disposed, hollow cylinder 72 which constitutes a second decelerator electrode. Decelerator electrode 72 is electrically connected to a second decelerator terminal 74. of the tube and defines a much larger diameter opening 76 than the axially aligned opening 70 in decelerator electrode The opposing end of the second decelerator electrode 72 is disposed adjacent the output end of envelope 16 which is closed by an output faceplate 80. The faceplate 80 is transparent .to visiblelight and, preferably, has substantially planar innerand outer surfaces, respectively. The output faceplate 80 may comprise a cylindrical bundle of fiber optic rods sealed in side by side relationship which, unlike glass faceplates, for example, prevents lateral spreading of a light image as it passes through a faceplate. Generally, a conventional X-ray image intensifier tube includes an input faceplate having a diameter in the range of 6 to l4 inches and an output faceplate having a diameter in the range of /2 to 1 inch, providing an input to output image ratio approximately in the range of 9 to 14 inches. However, this invention, in one of its operating modes, permits the input to output image ratio to be in the range of one and a third to four, for example, to provide an output image of suitable size and intensity for photographic cent material, such as silver activated zinc cadmium sulfide, for example, which is locally sensitive to impinging electrons. The fluorescent material of imaging screen 82, preferably, is deposited directly on the inner surface of output faceplate 80 in order to minimize intensity, resolution and contrast losses. The inner surface of imaging screen 82 is coated with athin conductive film 84 of light reflecting material, such as aluminum, for example, which is transparent to high energy electrons. Thus, the imaging screen 82 and the film 84 constitute an imaging screen assembly 86 having means for converting the electron image intoa corresponding visible light image which is viewable directly through the output faceplate 80, as by means of television camera tube 90, for example. The imaging screen assembly 86 extends radially into electrical contact with an inwardly extending flanged portion of a conductive anode ring 88. The anode ring 88 is circumferentially sealed to the periphery of output faceplate 80 and has an outwardly extending flanged portion which is hermetically attached, as by welding, for example, to the anode terminal 23 of the tube.

FIG. 2 illustrates typical electrode potentials for operating the image intensifier tube 14 in a direct viewing mode. Thus, the imaging screen assembly 86, preferably, is maintained at ground potential'and the photocathode 30 may be maintained at approximately a negative 25,000 volts with respect theretovThe grid electrodes 40, 44 and 54, respectively, are maintained at progressively less negative potentials than the photocathode 30 in order to establish accelerating electrostatic fields therebetween. These accelerating fields focus the electron image on a cross-over region located approximately between the first and second decelerator electrodes, 66 and 72, respectively. The first decelerator electrode 66 is maintained at a more negative potential than the third grid electrode 72 in order to espurposes. Therefore, in accordance with this invention,

the input faceplate 26 may have a diameter in the range of 9 to 14 inches, for example; and the output faceplate 80 may have a diameter in the range of 4 to 6 inches, for example.

Supported adjacent the inner surface of faceplate 80 is an imaging screen 82 comprising a layer of fluorestablish a decelerating electrostatic field therebetween. This decelerating field has the effect of bringing the outer marginal portions of the electron image to a focus in the same plane as the central portion of the image. After passing through the cross-over region, the electron image passes through the second decelerator electrode 72 which may be maintained at the same electrical potential as the imaging screen assembly 86.

As a result of passing through the accelerating electrostatic fields, the electron image acquires sufficient kinetic energy to pass through the conductive film 84 and impinge on the output screen 82. In the direct viewing mode, the electron image is incident on a minified central area, such as 1 inch in diameter, for example, of the output screen 82. Consequently, the output screen 82 fluoresces locally in direct proportion to the intensity of the impinging electrons thereby producing a corresponding minified, visible light image 92, as shown in FIG. 4. The minified output image 92 is much brighter than the associated visible light image produced by the input screen 28 not only because of the additional kinetic energy acquired by the accelerated electron image but also because of the reduction in image size. Since light energy in the visible image produced by the input screen 28 is ultimately concentrated in a smaller area of the output screen 82, there is a resulting increase in image intensity.

In radiographic imaging systems of the prior art, the amplification in image brightness achieved by minifying the image is advantageous in compensating for intensity losses which occur when the output image is magnified to the size of a photographic film, for example. However, due to the limiting grain size of fluorescent material comprising the output imaging screen, such extreme minification of the image causes adjacent fine structural detail therein to merge into one another thereby degrading resolution. Since a magnifying optical system cannot separate merged structural detail, valuable information available in the incident radiational image is not shown in the final photographic picture thereof. Therefore, in order to' preserve this information, the radiographc imaging system of this invention provides means for photographing the output visible image without requiring extreme image minification or an external magnifying optical system.

FIG. 3 illustrates typical electrode potentials for operating the image intensifier tube 14 in a film recording mode. Thus, the imaging screen assembly 86, preferably, is maintained at ground potential and the photocathode 30 may be maintained, for example, at approximately a negative 10,000 volts with respect thereto. The first and second grid electrodes, 40 and 44, respectively, are maintained at progressively less negative potentials than the photocathode 30 and the third grid electrode 54 is maintained at approximately ground potential, thereby establishing accelerating electrostatic fields between the aforesaid electrodes. These electrostatic fields focus the electron image emitted by the photocathode 30 onto a cross-over region within and adjacent to the third grid electrode 54. Afte passing through the cross-over region, the enlarging electron image enters a decelerating electrostatic field established by maintaining the first decelerator electrode 66 approximately at ground potential and the second decelerator electrode 72 at a relativelynegative potential, such as eight thousand volts negative, for example. After passing through the decelerating field, the still enlarging electron image passes through an accelerating field established between the negatively biased, second decelerator electrode 72 and the imaging screen assembly 86 maintained at ground potential.

As a result, the accelerated electron image passes through the conductive film 54 of imaging screen assembly 86 and'impinges on a larger area, such as four inches in diameter, fo'rexample, of the output screen 82 than in the direct viewing mode of operation. Consequently, in the film recording mode of operation, the output screen 82 produces an output visible image 94, as shown in FIG. 5, proportionate in size to the effective area of a conventional photographic ,film. However, since the minified output image 92 is spread out over a larger area of the imaging screen 82, the resolution is enhanced. Also, the radiographic imaging system of this invention provides means for pressing an aligned portion of a photographic film against the exterior surface of the output faceplate 80 while the film is being exposed to the output image 94.

As shown in FIGS. 1 and 4-7, a rectangular frame of rigid material, such as aluminum, for example, is attached, as by screws 102, for example. to the anode ring 88 such that the faceplate 80 is viewable through an end portion of the frame opening. Thus, the frame 100 has a transverse end wall 104 disposed adjacent the faceplate 80 and joins respective ends of longitudinal sides 106 and 108 which are disposed on diametric opposite sides of faceplate. The longitudinal sides 106 and 108 extend radially outward of the tube 14 and have respective other ends joinedby a transverse'end wall 1 10 which has a slot 112 therein. Attached to the longitudinal sides 106 and 108 are respective coextensive tracks 114 and l 16 which slidingly receive a film holding cassette 118 inserted through the slot 112. The cassette 118 comprises a light tightcontainer having therein a photographic film 120.and.havinga slidable cover 122.

In the direct viewing mode, the cassette 118 is positioned to one sideof the faceplate 80, as shown in FIGS. 4 and 6, so that the minified output image '92 may be studied, as with the aid of TV camera tube 90, for example. When the output image is to be photographed in the film recording mode, the cassette 118 is moved along the respective tracks 114 and 116 by conventionalmeans, such as an electrically operated drive mechanism (not shown), for example. When the cassette 118 is aligned with th output faceplate 80, the tube 14 is switched from the direct viewing mode to the film recording mode,as described. The cover 122 is slid back along the respective tracks 114 and 116 by any suitable means, such as electronically operated arm 124, for example, thereby exposing the film 120 to the expanded output image 94, as shown in FIG. 5. The film is pressed flat against the output faceplate 80, as shown in FIG. 7, by any convenient means, such as suitably located solenoids 126 having respective core ends urged'against the cassette 118 which functions as a pressure plate. The solenoids 126 may be required to overcome the resilency of return coil springs 128 pressing against the opposing side of the cassette 1.18. Thus, when the exposure is completed and solenoids 126 are deenergized, the springs 128 space the cassette 118 and film 120 away from the faceplate such that the cover 122 can be slid back over the film 120. Then, the cassette assembly may be moved along the respective tracks 114-116 and extracted through the slot 112;

By pressing the film against the exterior surface of output faceplate 80 during a photographicexposure, the maximum amount of light from the output image 94 is transmitted to the film 120 thereby producing a' bright clear pictureof the image. Unlike intensifier im-. aging systems of the prior art, the imaging system described herein does not require optical magnifying devices which reflect and absorb aportion of the output image light intensity. Also, the imaging system of this invention provides means fortime-sharing the output faceplate between the direct viewing mode and the film recording mode thereby eliminating the need for a beam-splitter which limits the quantity of light intensity reaching the photographic film. Furthermore, when practicing this invention, the resolution obtained in the resulting photograph is superior to that achieved by conventional intensifierjimaging systems, because the spacing between fine detailed structure in the expanded image 94 is greater than in the minified image 92, thus avoiding the loss of detail due to the limiting grain size of the output screen fluorescent material. Therefore, this invention provides means for producing more informative photographs of radiational images without increasing the intensity of the beam irradiating the subject 12.

9 Thus, therehas been disclosed herein an intensified radiographic imaging system including an image intensifier tube provided with an inputfaceplate and an output faceplate. The image intensifier tube also is provided with an input screen assembly which converts an incident radiational image into an electron image, an output screen assembly which converts the electron image into a visible light image, and an intermediate electrode structure having means for focussing the electron image onto a minified area of the output screen and alternatively onto an area of the output screen proportionate in size to the effective area of a photographic film in order to achieve optimum resolution characteristics. This system also includes pressure means for urging a photographic film of a size which may be readily examined without the aid of magnifying optical devices against the exterior surface-of the output faceplate, when desired, in order to transmit maximum light intensity from the output screen to the photographic film.

From the foregoing, it will be apparent that all of the objectives of this invention have been achieved by the structures shown and described. It will also be apparent, however, that various changes may be made by those skilled in the art without departing from the spirit of the invention as expressed in the appended claims. It is to be understood, therefore, that all matter shown and described is to be interpreted as illustrative and not in a limiting sense.

We claim:

1. An intensified radiographic imaging system comprising:

an image intensifier tube including an input screen assembly disposed to receive a radiational image of an external object and having means for emitting a corresponding electron image,

an output screen disposed to receive the electron image and having means for producing a corresponding visible light image, and

an output faceplate transparent to visible light and disposed adjacent the output screen;

' imaging recording means mounted externally of the tube and adjacent the output faceplate for permitting direct viewing and immediate sequential image recording of the output screen; and

means for focussing the entire electron image onto a portion of the output screen to produce a visible light image suitable for direct viewing through the output faceplate and alternatively electronically enhancing resolution and enlarging the output visible image for recording purposes.

2. An intensified radiographic imaging system as set forth in claim 1 wherein the means for electronically enhancing resolution, and enlarging of the output visible image includes focussing the entire electron image onto a relatively larger portion of the output screen.

3. An intensified radiographic imaging system as set forth in claim 2 wherein the image recording means includes a photographic film having an effective area of predetermined size.

4. An intensified radiographic imaging system as set forth in claim 3 wherein the larger portion of the output screen is proportionate in size to the effective area of the photographic film.

5. An intensified radiographic imaging system comprising:

an image intensifier tube including an input screen assembly disposed to receive a radiational image of an external object and having means for emitting a corresponding electron image,

an output screen disposed to receive the electron image and having means for producing a corresponding visible light image, and

an output faceplate transparent to visible light and disposed adjacent the output screen;

image recording media disposed externally of the tube and adjacent the output faceplate;

support means for positioning the image recording media with respect to the output faceplate in a manner permitting direct viewing of the output screen during selected intervals, and immediate image recording during alternate sequential intervals; and

focussing means for directing the entire electron image onto a portion of the output screen to produce a visible light image suitable for direct viewing through the output faceplate during the selected intervals and alternatively onto a relatively larger portion-of the output screen during the sequential intervals.

6. An intensified radiographic imaging system as set forth in claim 5 wherein the image recording media comprises a photographic film having an effective area.

7. An intensified radiographic imaging system as set forth in claim 6 wherein the positioning means includes means for aligning the film with the output faceplate and means for maximizing the light intensity reaching the film during the selected intervals.

8. An intensified radiographic imaging system as set forth in claim 7 wherein the means for maximizing light intensity includes pressure means for urging said effective area of the film against the exterior surface of the output faceplate.

9. An intensified radiographic imaging system as set forth in claim 8 wherein the size of said effective area of the film is at least substantially equal to said larger portion of the output screen.

10. An intensified radiographic imaging system comprising:

an image intensifier tube including an input screen assembly disposed to receive a radiational image of an external object and having means for emitting a corresponding electron image,

an output screen disposed in axial spaced relationship with the input screen assembly and having means for converting the electron image into a visi-' ble light image, and

an output faceplate transparent to visible light and disposed adjacent the output screen;

a photographic film disposed externally of the tube and adjacent the output faceplate in a manner permitting direct viewing of the output screen during selected intervals;

movable film support means for immediately aligning a portion of the photographic film with the output faceplate in a manner permitting image recording during alternate sequential intervals and pressing said portion of the film against the exterior surface of the output faceplate; and

focussing means for directing the entire electron image onto a portion of the output screen to produce a visual image viewable directly through the output faceplate during the selected intervals and alternatively onto a relatively larger portion of the 13. An intensified radiographic imaging system as set forth in claim 10 wherein'the output screen is supported on the inner surface of the output faceplate. v

14. An intensified radiographic imaging system as set forth in claim 13 wherein the electron image converting means includes a layer of fluorescent material disposed on the inner surface of the output faceplate.

15. An intensified radiographic imaging system as set forth in claim 14 wherein the output faceplate is a fiber optic element. 

1. An intensified radiographic imaging system comprising: an image intensifier tube including an input screen assembly disposed to receive a radiational image of an external object and having means for emitting a corresponding electron image, an output screen disposed to receive the electron image and having means for producing a corresponding visible light image, and an output faceplate transparent to visible light and disposed adjacent the output screen; imaging recording means mounted externally of the tube and adjacent the output faceplate for permitting direct viewing and immediate sequential image recording of the output screen; and means for focussing the entire electron image onto a portion of the output screen to produce a visible light image suitable for direct viewing through the output faceplate and alternatively electronically enhancing resolution and enlarging the output visible image for recording purposes.
 2. An intensified radiographic imaging system as set forth in claim 1 wherein the means for electronically enhancing resolution, and enlarging of the output visible image includes focussing the entire electron image onto a relatively larger portion of the output screen.
 3. An intensified radiographic imaging system as set forth in claim 2 wherein the image recording means includes a photographic film having an effective area of predetermined size.
 4. An intensified radiographic imaging system as set forth in claim 3 wherein the larger portion of the output screen is proportionate in size to the effective area of the photographic film.
 5. An intensified radiographic imaging system comprising: an image intensifier tube including an input screen assembly disposed to receive a radiational image of an external object and having means for emitting a corresponding electron image, an output screen disposed to receive the electron image and having means for producing a corresponding visible light image, and an output faceplate transparent to visible light and disposed adjacent the output screen; image recording media disposed externally of the tube and adjacent the output faceplate; support means for positioning the image recording media with respect to the output faceplate in a manner permitting direct viewing of the output screen during selected intervals, and immediate image recording during alternate sequential intervals; and focussing means for directing the entire electron image onto a portion of the output screen to produce a visible light image suitable for direct viewing through the output faceplate during the selected intervals and alternatively onto a relatively larger portion of the output screen during the sequential intervals.
 6. An intensified radiographic imaging system as set forth in claim 5 wherein the image recording media comprises a photographic film having an effective area.
 7. An intensified radiographic imaging system as set forth in claim 6 wherein the positioning means includes means for aligning the film with the output faceplate and means for maximizing the light intensity reaching the film during the selected intervals.
 8. An intensified radiographic imaging system as set forth in claim 7 wherein the means for maximizing light intensity includes pressure means for urging said effective area of the film against the exterior surface of the output faceplate.
 9. An intensified radiographic imaging system as set forth in claim 8 wherein the size of said effective area of the film is at least substantially equal to said larger portion of the output screen.
 10. An intensified radiographic imaging system comprising: an image intensifier tube including an input screen assembly disposed to receive a radiational image of an external object and having means for emitting a corresponding electron image, an output screen disposed in axial spaced relationship with the input screen assembly and having means for converting the electron image into a visible light image, and an output faceplate transparent to visible light and disposed adjacent the output screen; a photographic film disposed externally of the tube and adjacent the output faceplate in a manner permitting direct viewing of the output screen during selected intervals; movable film support means for immediately aligning a portion of the photographic film with the output faceplate in a manner permitting image recording during alternate sequential intervals and pressing said portion of the film against the exterior surface of the output faceplate; and focussing means for directing the entire electron image onto a portion of the output screen to produce a visual image viewable directly through the output faceplate during the selected intervals and alternatively onto a relatively larger portion of the output screen during the alternate sequential intervals.
 11. An intensified radiographic imaging system as set forth in claim 10 wherein said larger portion of the output screen is substantially equal in size to said pressed portion of the film.
 12. An intensified radiographic imaging system as set forth in claim 10 wherein the focussing means includes a coaxially aligned series of electrodes disposed in axial spaced relationship between the input screen assembly and the output screen.
 13. An intensified radiographic imaging system as set forth in claim 10 wherein the output screen is supported on the inner surface of the output faceplate.
 14. An intensified radiographic imaging system as set forth in claim 13 wherein the electron image converting means includes a layer of fluorescent material disposed on the inner surface of the output faceplate.
 15. An intensified radiographic imaging system as set forth in claim 14 wherein The output faceplate is a fiber optic element. 